Energy recovery apparatus for a gas compressor plant

ABSTRACT

This disclosure relates to apparatus for increasing the efficiency of a gas compressor plant by converting a portion of heat that is normally wasted into mechanical energy. The gas, when compressed, is heated due to the compression. The compressed and heated gas is passed through a cooler or heat exchanger where a portion of the heat of compression is transferred to a coolant. The heated coolant in turn is passed to a mechanical device where the heat energy is converted to useful mechanical energy.

This invention relates to gas compressor plants of the type that isprovided with an intercooler, or an after-cooler, or with both,generally for use in chemical plants.

As is well known, there are many manufacturing and processing plants,such as chemical plants, that require a facility for supplying gas underpressure, and FIGS. 1 to 3 show examples of such prior art gascompressor facilities. In FIG. 1, a drive such as on engine 1 is coupledto drive a turbine gas compressor 2. The gas intake of the compressor 2receives gas from a suitable source (not shown) and the high pressuregas outlet is connected to a gas cooler or heat exchanger 3. As shown inFIG. 1, the gas cooler 3 is provided at the outlet of gas compressor 2in many chemical plants so as to reduce the temperature of thecompressed gas. The temperature of gas is increased because of the heatof compression, and while the pressure is required, the increasedtemperature is usually undesired. For this reason, the compressed gas isusually cooled before use, and, for this purpose the cooler 3 isprovided. A coolant, such as relatively cool water, is moved through acoolant path in order to remove some of the heat from the compressedgas.

FIG. 2 shows a two-stage compressor wherein the compressor is separatedinto a low-pressure compressor stage 2-1 and a high-pressure compressorstate 2-2 in order to reduce the driving force required of thecompressor. The outlet of the low-pressure stage 2-1 is generallyequipped with a so-called intercooler 3 which cools the compressed gasand passes the cooled gas to the high-pressure stage 2-2, therebyreducing the driving force at the high-pressure compressor stage 2-2.

Some multiple stage compressors (FIG. 3) are equipped with both anintercooler 3-1 and with an after-cooler 3-2. In such gas compressorsprovided with an intercooler or an after-cooler, a high temperature ofthe compressed gas is unnecessary in the chemical plants utilizing ahigh-pressure compressor stage and an intercooler. Therefore, thecompressed air is cooled as described above.

In such conventional facilities, such coolers usually use sea-water orindustrial water, or they may use air where water is insufficient tocool the compressed gas. In other words, the thermal energy of thecompressed gas has been discharged outside the system as hot waste wateror waste gas in order that the temperature of the compressed gas may bethe desired value for the plant utilizing the compressed gas. From therecent viewpoint of saving energy, it is hardly necessary to say that itis further highly desirable to reduce the amount of power required todrive such a compressor. In the conventional compressor equipment shownin FIGS. 1 through 3, every possible effort has been made in the past toimprove the internal efficiency of the compressor. In such compressorsprovided with an intercooler as shown in FIG. 2 or FIG. 3, much efforthas been made not only to improve the internal efficiency of thecompressor, but also to decrease the temperature of the compressed gasat the outlet of the intercooler, or at the inlet of high-pressurecompressor stage, in order to decrease the driving force required. As apractical matter, however, it is impossible to decrease the gastemperature at the outlet of the intercooler below that of the coolant,such as cooling water. Besides, the internal efficiency of thecompressor cannot be improved any higher. Accordingly, in prior systemsthe driving force required for the compressor cannot be effectivelydecreased below a given limit. As explained above, this invention hasbeen made to overcome the limitation in the reduction of the drivingforce required for the compressor.

The quantity of heat exhausted through the intercooler or theafter-cooler has been large as will be described later. However, a largequantity of cooling water or cooling air has been used in an attempt todecrease the temperature of the compressed gas. Therefore, thetemperature of the cooling water or cooling air supplied through thecooler is relatively low. For instance, if the temperature of thecooling water to be supplied to the cooler is 25° C., the temperature ofthe cooling water released from the cooler is approximately 35° C. atmost. As shown, there is not a large difference between the temperatureof the cooling water or cooling air at the outlet of intercooler orafter-cooler of the conventional compressors, and that of the ambientair.

In the conventional compressors equipped with intercooler orafter-cooler, it can be concluded that it has been difficult to collectsuch waste heat having a minimum temperature difference, and the heatwas discharged outside the system and lost from the standpoint of heatbalance.

The purpose of this invention is to improve this situation. That is tosay, this invention may be realized by incorporating a closedrefrigerant circuit in which a refrigerant is circulated withoutdischarging the refrigerant to the outside of the system, and byproviding the refrigerant with cycles of phase change such asevaporation, expansion and condensation.

The purpose of this invention is to transfer the heat quantity containedin the compressed gas to the refrigerant, and to change the refrigerantphase cyclicly in the closed circuit, or to collect the heat by means ofthe refrigerant for use as a driving force in the process. In someembodiments, a turbine operated by the expansion of the refrigerant maybe incorporated in the closed refrigerant circuit to retrieve energy orpower through the refrigerant. A condenser may be also installed in theclosed refrigerant circuit, which liquefies the refrigerant so as tofurther increase the work output of the turbine, or power retrieved.

The heat energy contained in the compressed gas can be easilytransferred according to the following:

a. The refrigerant supplied from the condenser is condensed, and thetemperature of the refrigerant is satisfactorily decreased.

b. The heat exchanger (or cooler as viewed from the aspect of thecompressed gas) transferring the heat of the compressed gas to therefrigerant, is supplied with the refrigerant received from thecondenser.

c. The refrigerant is evaporated in the heat exchanger. As a matter offact, the refrigerant must produce a condenser temperature higher thanthe temperature of the cooling water at the pressure of the refrigerantwithin the condenser, and also the refrigerant must produce anevaporating temperature lower than the temperature of the saidcompressed gas at the pressure of refrigerant within the said heatexchanger.

The evaporating temperature and the condensing temperature of theequivalent refrigerants can be changed respectively by adjusting thepressure within the condenser, or the pressure within the heatexchanger, for refrigerant. It is more effective to minimize thepressure within the condenser for the refrigerant and to maximize thepressure within the heat exchanger, so as to better transfer the heatquantity of the compressed gas. Therefore, a pump is provided to returnthe refrigerant from the condenser to the heat exchanger. As clearlystated above, it is possible to increase not only the temperature, butalso the pressure of the refrigerant within the heat exchanger adjacentthe compressor. Thus, it is shown that the power can be easily collectedor retrieved by expanding the refrigerant. Consequently, it is possibleto easily collect the heat energy contained in the compressed gas.

If the power obtained through this method is applied as a part of thepower to drive the compressor, it becomes possible to greatly decreasethe capacity of the main driving unit 1 (FIG. 1) for the compressor 2.As explained above, the purpose of this invention is to effectivelycollect some of the heat energy of the heated compressed gas, which hasbeen wasted and further to effectively utilize the heat energy asmechanical power. This invention also helps to decrease the quantity ofheat being exhausted outside of the system, thereby improvingenvironmental conditions.

The recovered heat energy may be used to power a turbine, and theaddition of the mechanical output of the turbine to the main drive forthe compressor helps not only to reduce the required capacity of themain drive, but also helps to stabilize the operation for the drive ofthe compressor due to the fact that the output of turbine varies withthe load of compressor.

The invention may be better understood with reference to the figures ofthe accompanying drawings, wherein:

FIG. 1, FIG. 2 and FIG. 3 show schematic diagrams of conventional typesof compressor systems;

FIGS. 4 through 11 show schematic diagrams of specific examples of thepresent invention;

FIG. 12 (a), (b), (c) and (d) show arrangements of major rotary machinesaccording to specific examples of this invention;

FIG. 13, which is different from FIGS. 4 through 12, exemplifies anembodiment in which the mechanical output of a turbine according to thisinvention is supplied to drive a driven unit;

FIG. 14 is a simplified drawing of major parts showing a structuralmachine layout of a specific example according to this invention;

FIG. 15 is a schematic diagram of a multiple stage compressor grouphaving (n) number of intercoolers;

FIG. 16 shows graphs of calculated results of an example, expressing thedriving unit power as a function of the number of intercoolersinstalled; and

FIG. 17 shows a sectional drawing of an example of an axial flow typecompressor including a low-pressure compressor stage and a high-pressurecompressor stage.

FIG. 4 shows a specific example of this invention. In FIG. 4, T1, T2 andT3 represent the temperatures of the compressed gas at the respectivepoints, while T4, T5, T6, and T7 represent the temperatures of acirculating refrigerant at the respective points. A heat exchanger 3transfers part of the heat of the gas compressed by the compressor 2, toa refrigerant that flows in a closed circuit that includes the exchanger3. The refrigerant receives heat from the compressed gas without beingmixed with the compressed gas, and the transferred heat evaporates therefrigerant to a high-temperature gas which enters a turbine 4. Therefrigerant-gas expands in the turbine and drives it, and it then flowsto a condenser 5 which liquefies the refrigerant by cooling it. Thiscondenser 5 is cooled by, for example, cooling water supplied fromoutside the system (inlet temperature of water--T8, outlet temperatureof water--T9). The liquefied refrigerant is pumped by a pump 6 nd thenreturned to the heat exchanger 3. In this manner, the refrigerantcirculates through the heat exchanger, the turbine and the condenser,and thereby produces mechanical energy at the output of the turbine 4.

The output shaft of the turbine 4 is mechanically coupled to the shaftof the main drive 1 for the compressor 2 by, in this example, the shaftof the compressor 2. The gas compressed by the compressor 2 is passedthrough the heat exchanger 3, cooled to the temperature of T3, and thensupplied through a delivery pipe 7 to the plant (not shown) that willutilize it. To simplify the description, the plant that receives thecompressed gas is omitted from FIG. 4.

In the FIG. 4 system, the heat balance may be described in detail asfollows:

The power (Lc) required for the compressor 2 to compress the gas may beexpressed in thermal units as follows:

    Lc/unit weight flow rate of compressed gas=Cp (T2-T1)

where Cp is the specific heat constant at constant pressure of the gasto be compressed.

On the other hand, the heat quantity (Q) exchanged in the heat exchanger3 is given as follows:

Heat quantity (Q) for unit flow rate of compressed gas:

    Q=Cp(T2-T3)

In the usual case, the temperature (T3) required for a plant beingsupplied with the compressed gas is equal to T1 (the inlet temperatureof the gas being compressed by compressor 2). However, if T3 is equal toT1, Lc is equal to Q. This means that the temperature of the compressedgas does not attain the temperature (T3) which is required by the plantunless the heat quantity equal to the power driving the compressor 2 isextracted from the compressed gas. Even if T3 is not equal to T1, thesame theory applies. In the conventional compressors shown in FIGS. 1through 3, the heat quantity corresponds to the amount of heat disposedwastefully as waste heat. The heat quantity Q which is almost equal tothe power from the main drive 1, nevertheless helps to increase thetemperature of refrigerant in the heat exchanger from T7 to T4. In thisinstance, the refrigerant changes its phase or aspect from a liquid attemperature (T7) to gas at temperature (T4).

In other words, the refrigerant can easily be evaporated in the heatexchanger 3, thus easily permitting an exchange of heat. The refrigerantgasified by the heat exchanger 3 is supplied to the turbine to providethe expansion work LT as previously described. LT is the mechanicaloutput of the turbine 4, and helps to collect the heat quantity of therefrigerant effectively. The said refrigerant is not only cooled fromthe temperature (T5) to (T6), but it is also liquefied in the condenser5. The liquefied refrigerant at temperature T6 is returned to the heatexchanger 3 by the pump 6. If the heat quantity required to cool therefrigerant from T5 to T6 is Qc, and the power required to drive thepump 6 is Lp, then:

    Q=LT+Qc-Lp

where (LT-Lp) is the mechanical power collected effectively in thespecific example shown in FIG. 4. Therefore, it is possible to choosethe proper refrigerant, and further to determine the temperature and thepressure at each point in the system as far as (LT-Lp) is increased.Although this depends upon the cooling water temperature T8, it isadvisable to choose a freon gas or an ammonia gas as the refrigerant,depending on the temperature of T8 of the cooling water. Also, the aboveequation can be rearranged as follows: Qc=Q-(LT-Lp), which shows thatthe heat quantity (Qc) to be discharged or wasted outside of the systemis decreased with an increase in the power (LT-Lp) collectedeffectively. The decreased (Qc) to be discharged as waste water is alsosatisfactory from the viewpoint of environmental conditions. At the sametime, the decreased (Qc) requires less cooling water. In this sense,this invention contributes greatly to the construction of the equipmentat such places where the cooling water is not plentiful. As described,FIG. 4 shows a heat exchanger which directly transfers the heat of thecompressed gas to that of circulating refrigerant, and the heat transferis performed here without mixing the compressed gas with therefrigerant.

FIG. 5 shows another specific example of this invention applied to asingle stage compressor system as in FIG. 4. A first heat exchanger 3-1through which the heated compressed gas flows, is so constructed that ittransfers the heat of compression to a first refrigerant, and furthertransfers a quantity of the heat from the first refrigerant to a secondrefrigerant by means of a second heat exchanger 3-2. The firstrefrigerant is circulated in a closed circuit, indicated by the numeral3-3, which includes the two heat exchangers 3-1 and 3-2. If the circuit3-3, including the exchangers 3-1 and 3-2, is regarded as one heatexchanger, it corresponds to the heat exchanger 3 shown in FIG. 4. Alsothe second refrigerant corresponds to the refrigerant flowing throughthe turbine 4 shown in FIG. 4. A pump 3-4 circulates the firstrefrigerant through the closed circuit including the exchangers 3-1 and3-2, and a second pump 6 circulates the second refrigerant through theexchanger 3-2, a turbine 4, and a condenser 5. In the examples shown inFIG. 4, the turbine 4 is mechanically coupled to drive the turbinecompressor 2 and thereby assists the main drive 1.

In the specific example in FIG. 5, since the refrigerant used isseparated into the first refrigerant and the second refrigerant, eachrefrigerant can be optimally chosen, and therefore, the power collectedor retrieved in the turbine 4 can be more greater than that in FIG. 4.

FIG. 6 shows another specific example of this invention. As is evidentby comparing this example with the example shown in FIG. 4, in FIG. 6the refrigerant is stored in both the gas state or phase and in theliquid state which is not included in FIG. 4. In other words, agas/liquid drum or container 8 is included in the closed circuit inwhich the refrigerant in FIG. 6 is circulated. In FIG. 6, tworefrigerant circuits or loops 12 and 13 are provided, both circuitsincluding the drum 8. The first circuit 12 includes a coil 14 in theexchanger 3, a pump 15 and the drum 8, whereas the second circuit 13includes another coil 16 in the exchanger 3, the drum 8, the turbine 4,a condenser 5 and the pump 6. The lower part of the drum 8 is filledwith liquid refrigerant and the upper part is filled with gaseousrefrigerant. The outlets of both coils 14 and 16 are connected todeliver the heated refrigerant to the drum 8, and the intake of theturbine 4 is connected to the upper part of the drum 8 so as to receivethe refrigerant in the gaseous state. In this example, the heat transferbetween the gas compressed by the compressor and the refrigerant can beperformed more effectively than the example shown in FIG. 4. In FIG. 6,it is possible not only to select the piping route to permit effectiveheat transfer to the refrigerant when the temperature of the compressedgas is decreased from T2 to T3, but there also is provided a stabilizedoperation throughout the entire system, because the load fluctuations(producing a fluctuation of the temperature T2) do not directlyinfluence the operation of the turbine 4. The specific example shown inFIG. 7 is arranged such that the liquefied refrigerant accumulated inthe gas/liquid drum 8 is supplied to the different input stages of amulti-stage turbine 4. Since the refrigerant pressure at the turbinestages is during its expansion process, it is lower than the pressure inthe cylinder drum 8. The refrigerant supplied to the different stage iseasily expanded in succession toward the outlet of the turbine,resulting in that the turbine power output is increased. When the systemis constructed as shown in FIG. 7, it should not be necessary to saythat the appropriate refrigerant must be chosen.

The FIG. 7 system includes the components of FIG. 6 except that theturbine in FIG. 7 has multiple input stages, and it also includesanother refrigerant circuit 17. The circuit 17 includes the coil 16, thedrum 8, two small drums 9 and 18, and a pump 19. Flow control throttles10 and 20 are respectively connected between the drums 8 and 9 andbetween the drums 9 and 18. The drum 8 is connected to supplyrefrigerant to the drum 9 and the drum 9 supplies refrigerant to thedrum 18. The two small drums have gas outlets connected to intermediateinputs 21 and 22 of the turbine 4. The drum 18 also has an outputconnected to the pump 19 and to the coil 16. If only one intermediate ormiddle input stage 21 is on the turbine 4, only the drum 9 need beprovided, and both drums 9 and 18 are provided when multiple middleinputs are included.

When the refrigerant is to be supplied to only the middle stage 21 ofturbine, the small drum 9 is attached, and the refrigerant is lead to itfrom the gas/liquid drum 8 through suitable piping. If the proper flowthrottle 10 is equipped in the piping to control the pressure, therefrigerant is boiled in the said drum 9 due to decreased pressure,whereby the refrigerant is easily gasified before entering the middlestage of the turbine 4. If the turbine includes the two middle inputs 21and 22, both of the small barrels 9 and 18 are provided. Severalspecific examples have been described so far. It will be apparent that avariety of other examples can be realized by combining the examples. Asshown in FIGS. 4 through 7, a common feature of this invention is thatthe heat transfer is performed between the compressed gas and therefrigerant without the two being mixed, and that the refrigerant iscirculated within a closed circuit.

Another feature is that the heat transfer between the compressed gas andthe refrigerant is performed so as to evaporate the refrigerant eitherpartially or totally. If the portions of the system closed in the boxes23 formed by the dash-dot lines in FIGS. 4 through 7 can be regarded asone heat exchange system in each figure, the refrigerant passing throughthe turbine 4 and the condenser 5 is circulating in one closed circuit.However, the fact remains that the refrigerant receives the heat fromthe gas compressed by the compressor.

The specific example shown in FIG. 8 is a case wherein the gascompressor is separated into a low-pressure compressor stage 2-1 and ahigh-pressure compressor stage 2-2. The shafts of the two stages 2-1 and2-2 are coupled together and to the main drive 1 and the recoveryturbine 4. This specific example is provided with a first heat exchanger3-1 which transfers a heat quantity from the gas compressed by thelow-pressure compressor 2-1 (the exchanger 3-1 corresponds to anintercooler from the viewpoint of the gas compressor), and with a secondheat exchanger 3-2 which transfers a heat quantity from the gascompressed by the high-pressure compressor 3-2 (the exchanger 3-2corresponds to an after-cooler).

The refrigerant is moved by the pump 6 through the two exchangers 3-1and 3-2 which are connected in parallel between the pump and the turbine4.

This arrangement corresponds to an extended version of the system ofFIG. 4. Also, the specific example shown in FIG. 9 corresponds to anextended version of the system of FIG. 8. With reference to FIG. 9 whichalso shows a multiple stage gas compressor, the pump 6 moves therefrigerant through a single exchanger 3-3. The heated, compressed gasis passed through two exchangers 3-1 and 3-2. The latter exchangers 3-1and 3-2 are connected in parallel from the view of the refrigerant, andthey both feed refrigerant to the exchanger 3-3. Thus there are twoseparate refrigerant circuits. Another possible specific example, shownin FIG. 10, a cylinder or drum 8 as shown in FIG. 6 is combined with anintercooler 3-1 and after-cooler 3-2 connected as shown in FIG. 8 andFIG. 9. Similarly, in still another specific example of this invention asmall drum 9 as shown in FIG. 7, is provided to supply the gaseousrefrigerant to a middle input stage of the turbine 4, in a system asshown in FIG. 10.

The next specific example of this invention is shown in FIG. 11, whereina heat quantity of the compressed gas is transferred to a firstrefrigerant e.g., water (H₂ O) in a heat exchanger 3-1. The firstrefrigerant supplied with the heat quantity operates to vaporize asecond refrigerant e.g., ammonia (NH₃) that is dissolved in the firstrefrigerant. The temperature of the gaseous or vaporous secondrefrigerant may be decreased by cooling water supplied from outside in aheat exchanger 10. Then, the gaseous second refrigerant is supplied tothe turbine 4, where it is expanded. Thereby, not only does the turbineprovide mechanical output, but also the temperature of the secondrefrigerant is lowered substantially due to expansion in the turbine.The second refrigerant leaves the turbine and is connected to anexchanger 3-2 to further cool the compressed gas fed from the heatexchanger 3-1 down to the temperature T10. The second refrigerantleaving the heat exchanger 3-2 is fed to the condenser 5. The condenser5 is so designed that after the second refrigerant is vaporaized orevaporated in the heat exchanger 3-1, the first refrigerant with a weaksolution of the second refrigerant is led to the condenser 5. Thecondenser 5 is cooled by the external cooling water. The firstrefrigerant, the temperature of which is decreased in the condenser 5,can easily absorb the gasified second refrigerant leaving the secondheat exchanger 3-2. (It is advisable to choose a second refrigerantwhich has greatly different dissolving performances in the firstrefrigerant.) Therefore, the said second refrigerant is absorbed by thefirst refrigerant in the condenser 5, and is held in such conditionwhere it is dissolved in the first refrigerant, or in solution in thefirst refrigerant. In other words, the condenser 5 operates to transformthe vaporized second refrigerant into the liquid phase in the firstrefrigerant. The first refrigerant containing the dissolved secondrefrigerant at a higher concentration, is returned to the other heatexchanger 3-1 by the pump 6. In this manner, the second refrigerantrepeats the vaporization and absorption processes as it circulates inthe closed circuit, including the exchanger 3-1, the turbine 4, and thecondenser 5. This powers the turbine 4, thereby retrieving or collectinga heat quantity of the gas compressed by the compressor 2. In thespecific example shown in FIG. 11, it is possible not only to vary thedegree of dissolution of the first refrigerant in accordance with thetemperature, but also to select a liquefaction temperature far lowerthan that of external cooling water according to the condition at theoutlet of the turbine 4. For this reason, it is possible to decrease thegas temperature (T10) to a value lower than the temperature (T8) of theexternal cooling water. In this case, as a matter of fact, the volume ofexternal cooling water fed to the condenser 5 and to the cooler 10 atthe inlet of the turbine, is larger than that required in the specificexample shown in FIG. 4.

The principle of the example shown in FIG. 11 is especially effectivewhen applied to a facility of the character shown in FIG. 2. In otherwords, suppose that the delivery pipe 7 shown in FIG. 11 is followed bya high-pressure second stage compressor as shown in FIG. 2, thetemperature T10 can be decreased to a value lower than the temperatureT8 of the external cooling water, and this means that the driving forcerequired for the high-pressure compressor will be lower than thatrequired for the system shown in FIG. 2. (The driving force required bya compressor is proportional to the absolute temperature of the gas tobe compressed, at the inlet of the compressor. This is the basis for theinstallation of an intercooler in a multi stage compressor.)

As clearly described above, if the principle of the invention shown inFIG. 11 is applied to a system having an intercooler as shown in FIG. 2,it is possible not only to collect or retrieve the power in turbine 4,but also to decrease the driving force required for high-pressurecompressor stage, with the result that the capacity of the main drive 1may be greatly reduced. The heat exchanger 10 shown in FIG. 11 isprovided to decrease the outlet temperature (T5) of the turbine bydecreasing the inlet temperature (T4) of the gas entering the turbine.In other words, the exchanger 10 is provided to decrease the temperature(T10) of gas in the delivery pipe 7. If it is not necessary that thetemperature (T10) be lowered further, the cooler 10 may be eliminated,and the heat exchanger 3-2 also may not be required. It is desirable toinstall a flow control throttle 11 in the piping carrying the firstrefrigerant from the heat exchanger 3-1 to the condenser 5 as shown inFIG. 11 so as to control the pressure level.

It should be obvious that the principle of the example shown in FIG. 11,wherein the refrigerant used is a mixture of first and secondrefrigerants, can be also applied to the examples of this inventionshown in FIGS. 9 and 10. In either case, the system can be constructedby combining the piping circuit so that a quantity of the heat of thegas compressed by compressor is transferred to the refrigerant.

The following is an explanation of detailed examples showing how themechanical output of the energy retrieved or collection turbine isutilized. FIGS. 4 through 11 show examples wherein a main drive 1, acompressor or compressors and a turbine 4 are direct-coupledmechanically. In other words, the foregoing are examples in which themechanical output (the mechanical rotating force) is connected directlyto the rotating shaft of the gas compressor. In such a case, the systemneed not be arranged in the order of a driving unit 1, a compressor 2,and a turbine 4, as shown in FIG. 12(a). It is also possible to arrangethe system in the order of a turbine 4, a driving unit 1, and acompressor 2, as shown in FIG. 12(b). FIGS. 12(c) and 12(d) showdifferent arrangements of a multiple stage gas compressor. In FIG. 12,the heat exchanger, the condenser and the closed refrigerant circuit areomitted in order to simplify the drawings but, of course, they would beprovided in accordance with one of the previously described examples ofthe invention. It is also possible to install a gear coupling such as astep-up or step-down gear connection between the driving unit 1, thecompressor and the turbine 4 as necessary to meet specific requirements.If an engagement disengagement type (for instance a clutch type)coupling is provided in between components, for instance, and if thesystem is so designed that the turbine 4 can be separated from the othercomponents, the maintenance and inspection of the system can beperformed with ease.

In addition, if a bypass pipe (not shown) is provided in the examples ofthis invention shown in FIGS. 4 through 11 around the turbine 4 so thatthe refrigerant fed to the turbine 4 can be bypassed around the turbinewhen desired, the compressor can be operated when the turbine 4 isseparated. In this case, even if the turbine 4 is ineffective for somereason or other, the plant can still be supplied with the compressed gasat the specified reduced temperature, which ensures a safer system.

The following is a description of a specific example in which theturbine 4 is not directly connected to the compressor or to the maindriving unit 1. The refrigerant system shown in FIG. 13 is similar tothat shown in FIG. 4. As shown in FIG. 13, the recovery turbine 4corresponding to the turbine 4 in FIG 4, is coupled with another drivenunit 24 such as a generator or a pump, and they are not mechanicallyconnected to the main drive 1 and the gas compressor 2. In this case,the capacity of the driving unit 1 of the compressor 2 is not differentfrom that for a conventional compressor, but the power to drive thedriven unit 24 is provided by the recovered energy in accordance withthis invention, and the amount of the power collection is significant.For instance, the driven unit 24 described above can be an electricalgenerator that supplies power to a chemical plant where the compressorequipment is installed. This example not only brings about as a directresult a saving in the energy required by the plant, but it also enablesone to collect or retrieve power in an amount that is proportional tothe amount of power consumed by the compressor 2, thus stabilizing theenergy consumption within the plant.

FIG. 14 shows a structural arrangement for the example shown in FIG. 4.FIG. 14 shows in side view a driving unit 1, a compressor 2 and aturbine 4 installed on a structural foundation shown by diagonal lines.In this example, the heat transfer is performed from the compressed gasto the refrigerant, and therefore, the heat exchanger 3 can be locateddirectly under or very close to the outlet of compressor 2. Since theturbine 4 can be direct-coupled to the compressor 2 shaft as statedabove, it is also possible to obtain a very compact arrangement. Thispermits one to obtain an effective power collection without anyrestrictions or ill effects upon the arrangement of compressor 2, whichis one essential function of this invention. Although the piping, thepump 6, etc. are shown in simplified form in FIG. 14, this example ischaracterized in that the heat exchanger 3 is located right under (orclosely beside) the compressor 2, and the condenser 5 is located rightunder (or closely beside) the turbine 4. This compact installationenables one to minimize the pressure loss of the compressed gas and therefrigerant. At the same time, the system of FIG. 14 is arranged on theassumption that the compressor 2 is a so-called axial flow compressor,and that the turbine 4 is also an axial flow type turbine. The drivingunit 1 is assumed to be an electric motor. In such an application, it isvery easy to direct-couple the driving unit 1, the compressor 2 and theturbine 4. This application enables one to design a layout that does notinclude a step-up or step-down speed gearing, thus providing aneffective arrangement. (The mechanical loss is further reduced ascompared with the case where a change-speed gearing is provided.Besides, the shafts of the system will never cause vibration, etc.) FIG.14 shows structural arrangement illustrating that such equipment can bearranged in a compact manner. The example further proves that thisinvention is not accompanied by harmful effects in its construction.

FIG. 15 shows an example of a conventional multiplestage compressorsystem which is divided into (n) number of intercoolers, (n+1) number ofgas compressors, and an aftercooler provided at the outlet of the lastcompressor stage. The graph of FIG. 16 shows an example of the powerrequired of the driving unit, indicated by the solid line (a) when (n)number of intercoolers and one after-cooler are installed in aconventional system as shown in FIG. 15. FIG. 8 shows a specific examplein which one intercooler and one after-cooler are provided. An exampleof the power requirements for the driving unit is shown in FIG. 16 bybroken lines (b). Comparing the line (a) for a conventional system withthe line (b) for a system using this invention, it will be apparent thatthere are considerable savings by utilizing this invention. Although thecurves shown in FIG. 16 may vary slightly according to the conditionsapplied to the compressor, it is customary that three intercoolers areenough to minimize the power of the driving unit 1 in a conventionalsystem. In the specific examples using this invention, on the otherhand, it is the customary case that the driving unit power output can beminimized effectively using one intercooler. If the number ofintercoolers is increased, with the pressure in the entire compressorsystem held at a constant level, it suddenly becomes difficult tocollect the power according to this invention, because the temperaturelevel of the compressed gas is decreased at the outlet of eachcompressor. For this reason, the installation of one intercooler isoptimum when the specific example of this invention is applied as shownin FIG. 16. In other words, the casing of a conventional type ofcompressor was divided into four portions or so to permit the insertionof three intercooler units, which was optimum from the viewpoint ofpower needed for driving unit. However, the driving unit power can befurther reduced by dividing the compressor casing into two portions toequip a turbine, etc. with one intercooler inserted. Thus, the reducednumber of divided portions of compressor contributes not only to areduction in the driving power, but also to a simplified construction ofcompressor, thus providing easy maintenance and inspection, and furtherimproving the reliability of the compressor. Especially when thecompressor being used is an axial flow type compressor, this provides anessential factor enabling a reduction in the number of the dividedportions of compressor. In other words, although a compressor of theaxial flow type is constructed substantially long in axial direction, itbecomes extremely long in the axial direction as the portions occupiedby the infusers or diffusers are increased when the compressor isdivided into many casing portions. On the other hand, this inventionpermits one to use only two casings without fear of causing vibration,etc. in the shaft system, and it is very desirable in many applications.

FIG. 17 is a sectional drawing of an example for an axial flow typecompressor constructed with two casings. In FIG. 17, only the majorcomponents are covered in order to simplify the description, and theheat exchanger and the turbine are omitted. The low-pressure compressor2-1 and the high-pressure compressor 2-2 are provided with an inducer(i) and a diffuser (d) respectively. In such an example where the systemis constructed including a driving unit 1 and an axial flow typecompressor 2-1 and 2-2, the number of intercooler 3-1 required to beinstalled is limited. Thus, this invention requiring at most oneintercooler unit 3-1 is more effective in such an application example asstated above.

In the following, the validity and importance of this invention is to bedescribed from another point of view. In the compressor constructed asshown in FIG. 3, for instance, the inlet gas temperature of thehigh-pressure compressor stage was reduced by the intercooler 3-1 inorder to reduce the driving unit power requirement in the conventionalsystem. This illustration includes the case where the gas compressed bythe compressor is ordinary air. In such a case, the moisture content ofthe compressed air was usually partly condensed when the air is cooledin the intercooler. A part of the condensation, or small liquiddroplets, was usually fed to the high-pressure compressor together withthe compressed gas, resulting in so-called condensation attack at theimpeller of the high-pressure compressor.

In the specific example of this invention shown in FIG. 8, however, thecompressed gas supplied from the heat exchanger 3-1, corresponding to anintercooler is cooled to such a temperature level at which nocondensation is caused before it is supplied to the high-pressurecompressor. Although the power of the high-pressure compressor isslightly increased in this case, the quantity of heat collected from theheat exchanger corresponding to an after-cooler is increased due toincreased humidity of the compressed gas at the outlet of thehigh-pressure compressor, thus resulting in increased amount of power tobe collected or retrieved by the turbine 4. This permits a reduction inthe driving unit power in the entire compressor system to a value farlower than that in the conventional system shown in FIG. 3. It alsomakes it possible to select a temperature level which does not allow thegeneration of condensation at the inlet of the high-pressure compressor,resulting in the elimination of condensation attack in the high-pressurecompressor.

If a compressor systems handling a gas component such as hydrogensulfide (H2S) which may promote corrosion properties due to the presenceof condensation, it can be said that this invention fulfills anessential action.

As explained concretely in the above specific examples, the systems isso constructed that the turbine is operated by the power resulting fromthe circulating refrigerant, with a quantity of the heat of the gascompressed by the compressor as a heat source. Therefore, it has becomepossible to collect the waste heat which previously was disposed aswaste heat in the conventional systems. In addition, the invention makesit possible to effectively utilize the energy collected, as a mechanicaloutput, which makes it possible to greatly reduce the amount of powerrequired for the main driving unit, or to apply the power directly tothe equipment requiring such power. It is also possible to decrease thequantity of the cooling water to be cooled from outside, by a quantitycorresponding to the power collected. It may be also possible to coolthe gas compressed to a value lower than the temperature of the outsidecooling water. It is easy to maintain the temperature of the compressedgas at the temperature required for the plant utilizing the gas. It isalso an important effect of this invention that the power collected isincreased in proportion to the load applied to the compressor, whichhelps to stabilize the operation of the entire system. As stated above,this invention also enables the elimination of condensation attack,which accompanies the essential effects as described in the foregoing.

What is claimed is:
 1. In a gas compression plant including a gascompressor driven by a main drive, the compressor including a gas intakeand a compressed gas outlet, the improvement comprising a refrigerantcircuit connected to said gas outlet, said refrigerant system includinga heat exchanger connected to receive said compressed gas, a turbine, acondenser, and a pump for circulating said refrigerant through saidcircuit, said refrigerant being heated and vaporized in said heatexchanger by a quantity of heat received from said compressed gas, andsaid vaporized refrigerant expanding in and driving said turbine andbeing liquefied in said condenser.
 2. Apparatus as in claim 1, whereinthe power output of said turbine is connected to drive said gascompressor.
 3. Apparatus as in claim 1 or 2, wherein the gas compressoris a multiple stage compressor, and said refrigerant circuit includes aheat exchanger between adjacent stages of said compressor.
 4. Apparatusas in claim 3, wherein said refrigerant system further includes anafter-cooler connected to the last of said multiple stages.
 5. Apparatusas in claim 1, wherein said turbine is coupled to drive a device whichis separate from said compressor.
 6. Apparatus as in claim 1 or 2,wherein said refrigerant circuit further includes a barrel and saidcircuit is divided into first and second refrigerant paths, said firstpath including said heat exchanger, said barrel, said turbine, said pumpand said condenser, and said second path including said heat exchangerand said barrel, said first and second paths merging in said barrel. 7.Apparatus as in claim 6, wherein said turbine has multiple input stages,and said refrigerant circuit further includes a second barrel connectedto said first-mentioned barrel, to an intermediate input of saidturbine, and to said heat exchanger.
 8. Apparatus as in claim 3, whereinsaid refrigerant flows in parallel in said heat exchangers.
 9. Apparatusas in claim 1 or 2, wherein said refrigerant circuit includes first andsecond paths and first and second refrigerants flowing in said paths,one of said refrigerants being dissolved in the other of saidrefrigerants, said first path including said heat exchanger, saidturbine and said condenser, and said second path including said heatexchanger and said condenser, both of said refrigerants circulating insaid heat exchanger and in said condenser, and one of said refrigerantsbeing dissolved in the other of said refrigerants.